The present invention relates generally to apparatus, systems, and methods for isolating Plain Old Telephone Service (POTS) signals from higher band communication signals and, more particularly, for apparatus, systems, and methods for isolating POTS signals from Asymmetric Digital Subscriber Line (ADSL) signals.
In general, modems designed for use with conventional telephone lines accommodate relatively low data transmission rates. While current modems can process a high-end bit rate at about 33.6 Kbits/second, they are nonetheless significantly slower than a digital modem, such as one on an ISDN line which can operate at 64 Kbits/second. These rates, unfortunately, remain too low for many desired types of communication, such as full-motion video which requires a minimum of 1.5 Mbits/second for VHS quality using MPEG-1 (Motion Pictures Expert Group) compression and 3 to 6 Mbits/second for broadcast quality using MPEG-2 compression.
A recently pronounced standard in telecommunications defines an Asymmetrical Digital Subscriber Line (ADSL) system which executes a high speed transfer of data over a single twisted-wire pair, such as an existing telephone line. In addition to Plain Old Telephone Services (POTS), an ADSL system also permits full-duplex and simplex digital services with data rates from about 1.5 Mbits/second to 7 Mbits/second. An ADSL system uses a spectrum from about 26 kHz to 1.1 MHz for broadband data transmission and leaves the spectrum from about DC to 4 kHz for POTS. An ADSL system provides at least four downstream simplex channels having rates ranging from about 1.5 Mbits/second to 6 Mbits/second and four full duplex channels with rates ranging from about 64 Kbits/second to 640 Kbits/second. An ADSL system is therefore more than capable of providing video-on-demand capability, video conferencing, data file transfer capability and can provide all of this capability simultaneously with POTS. For additional information, reference may be made to American National Standards Institute Standard ANSI-T1.413-1995 which describes an ADSL system and an interface between a telecommunications network and a customer""s installation and which is incorporated herein by this reference.
With reference to FIG. 1, a standard ADSL system 10 may comprise an ADSL transceiver unit 12 at a central office (ATU-C) which communicates with an ADSL transceiver unit 14 at a customer premises (ATU-R). The ADSL transceiver unit 12 at the central office receives data from a digital network 15, performs various processing on the data, and transfers the processed data to a splitter 16. The splitter 16 combines the signals from the transceiver unit 12 with signals from a public switched telephone network (PSTN) 18 and transfers the combined signals onto a line 20. At the customer end, a splitter 22 supplies a lower-band set of signals to one or more POTS terminal devices 24 and a higher-band set of signals to the ADSL transceiver unit 14. The ADSL transceiver unit 14 at the customer""s end processes the received signals and supplies the processed signals to one or more service modules (SM) 26. The processed data from the ADSL transceiver unit 14 may be supplied directly to the one or more service modules 26 or may be supplied through a customer installation distribution network 28. The network 28 may be any type of network, such as a star or bus network. Reference may be had to ANSI T1.413-1995 for additional information on the ADSL transceiver units 12 and 14 and on other aspects of the ADSL system 10, which is hereby incorporated by reference.
One difficulty with ADSL, however, is that the signals supplied to the ADSL transceiver 14 and the signals supplied to the POTS terminal device 24 must be isolated from each other. One reason requiring this isolation is that the POTS terminal device 24, which may be a telephone or other non-linear device, produces inter-modulation harmonics from the ADSL system both in the frequency range of the ADSL signals and in the voice band. Likewise, the ADSL transceiver unit 14 can generate interference with the signals supplied to the POTS terminal devices 24. Consequently, some type of filtering must occur between the ADSL transceiver 14 and the POTS terminal devices 24.
The signals supplied to the POTS terminal devices 24 may be isolated from the signals supplied to the ADSL transceiver unit 14 in any one of a multitude of ways. One of these ways is to place a low-pass filter at each POTS terminal device 24 and to place a high-pass filter at either the ADSL transceiver unit 14 or at a network interface device (NID). For instance, the low pass filters may be placed in series between the POTS terminal devices 24 and their connection to a wall jack. These low pass filters would then filter out the higher band ADSL signals and prevent the ADSL signals from interfering with the POTS signals.
The placement of the low-pass filter at each POTS terminal device, however, adversely affects the overall performance of the ADSL system 10. The lines connecting the POTS terminal devices 24 to the low pass filters look like bridge taps to the ADSL line and produce significant losses at the top end of the downstream ADSL band transfer function, such as losses from 5 dB to 15 dB between 400 kHz and 1.1 MHz. The reason for these losses and their effects on the ADSL system 10 are explained in more detail in Dennis J. Rauschmayer, xe2x80x9cEffects of a Distributed POTS Splitter Topology on ADSL Line Transfer Functions,xe2x80x9d American National Standards Institute T1E1.4 Technical Subcommittee Report T1E1.4/96-167, Jul. 22, 1996, which is incorporated herein by this reference. The placement of low-pass filters at each POTS terminal device 24 is therefore undesirable due to their effects on the ADSL signals.
In contrast to the placement of a low-pass filter at each POTS terminal device 24, the use of a single low pass filter for all POTS terminal devices 24 produces more favorable results. For instance, a comparison between the placement of the low-pass filter at each phone drop versus the placement of the low-pass filter at a split is described in a report by Rick Roberts et al., xe2x80x9cADSL POTS LPF Placement,xe2x80x9d American National Standards Institute Working Group Report T1E1.4/96-162, July, 1996, which is incorporated herein by this reference. This report suggests that a single low-pass filter at the split is preferred since a distributed low-pass filter at each phone causes several problems, such as a reduced bit rate and reduced reach of the ADSL system, an increase in line driver current, a hybrid/echo cancellation stress, and risk of improper installation or improper network modification. Thus, rather than placing a low-pass filter at each POTS terminal device 24, the ADSL system 10 should preferably have a single low-pass filter installed at the split so that the signals supplied to all of the POTS terminal devices 24 are filtered by this single low pass filter.
A single low-pass filter, however, is not as easily installed at a split as are multiple low-pass filters at each POTS terminal device 24. With multiple low-pass filters, a low-pass filter can be easily incorporated to the telephone network by simply adding a filter between each POTS terminal device 24 and its connection to the customer""s telephony wiring, such between the POTS terminal device 24 and a wall jack. The single low-pass filter, on the other hand, must be located at a point along the customer""s wiring which is shared by all POTS terminal devices 24 but not at a location which might affect ADSL signals traveling to and from the ADSL transceiver unit 14.
When the customer""s premises is an apartment, adding a low-pass filter to the telephony wiring becomes especially difficult. A typical wiring diagram 30 for an apartment is shown in FIG. 2. The wiring 30 for an apartment includes an inside network interface (xe2x80x9cINIxe2x80x9d) 32 within which is contained a customer demarcation point. The customer demarcation point often comprises a testing jack 36 having a female jack 36A receiving tip and ring signals from the central office (xe2x80x9cCOxe2x80x9d) and a male jack 36B connected to lines 38A and 38B. The tip and ring signals provided on lines 38A and 38B are provided to a red (xe2x80x9cRxe2x80x9d) terminal and a green (xe2x80x9cGxe2x80x9d) terminal which carry the tip and ring signals over R and G lines 39A and 39B, respectively, to telephone jacks 34 within the apartment. Each of the telephone jacks, which commonly are RJ11 jacks, is connected in parallel to the other telephone jacks through the R and G lines 39A and 39B and each receives the tip and ring signals from the INI 32. Although two telephone jacks 34 have been shown, an apartment may comprise any number of telephone jacks 34. Each telephone jack 34 has a pair of lines 42A and 42B respectively connected to the R and G terminals, and consequently to the R and G lines 39A and 39B, for carrying the tip and ring signals to a female connector 44 of the RJ11 jack 34. A corresponding male connector of a POTS terminal device 24, such as a male RJ11 connector, may be inserted within the female connector 44 to carry telephony signals to the POTS terminal device 24.
As discussed above, a single low-pass filter is preferably installed within the customer""s telephony wiring in order to provide filtering for all POTS terminal devices 24. One possible location for the low-pass filter is between the female connector 36A of the testing jack 36 and the R and G terminals within the INI 32. The INI 32, however, is a small enclosure and does not have any space to receive a low-pass filter. The INI 32 is often located within the kitchen of an apartment and includes a wall-mounted RJ11 telephone jack 34, whereby it would be both difficult and expensive to replace or modify the INI 32 to incorporate a low pass filter. A suitable location for the low-pass filter is therefore difficult to find within an apartment.
An apartment presents other problems as well in installing a low pass filter for ADSL services. For instance, tenants of apartments are relatively transient and frequently do not stay within a particular apartment for a prolonged period of time. If a tenant desires ADSL services, as discussed above, the wiring within the apartment must be modified to incorporate the low pass filter. The landlord and tenant may be unwilling to make the change in the wiring if it would require a substantial amount of work to the premises or if it would involve a significant cost. Additionally, some landlords may be unwilling to authorize the change if the apartment could not be easily reverted back to a POTS only service. Any change to the customer""s wiring 30 to accommodate ADSL service should therefore be easy and inexpensive to install and should be easily reconverted to POTS only service.
The problems discussed above with reference to modifying the customer""s wiring 30 to include a low-pass filter is not limited to apartments but applies to any residential or commercial building. Moreover, the problems of installing a low-pass filter are not limited to INIs 32 but are endemic to other types of interface devices, such as an outside network interface (xe2x80x9cONIxe2x80x9d) device, any network interface device (xe2x80x9cNIDxe2x80x9d), as well as in locations not having any type of interface device.
The present invention solves the problems described above by providing apparatus, systems, and methods for isolating POTS signals from higher band communication signals, such as ADSL signals. In a customer""s telephony wiring, incoming calls are customarily routed to red and green lines of the wiring and all telephone jacks are wired to receive POTS signals over these red and green lines. With the invention, the incoming calls, including the POTS signals and the ADSL signals, are provided to blue and yellow lines of the customer""s telephony wiring. A low pass filter is connected so that its input is connected to the blue and yellow lines and its output is connected to the red and green lines. The low pass filter removes the ADSL signals from the POTS signals and provides filtered POTS signals over the red and green lines to all telephone jacks within the customer""s telephony wiring. The ADSL signals are received over the blue and yellow lines and are provided to a transceiver unit.
In the preferred embodiment, the switching of the incoming calls from the red and green lines to the blue and yellow lines occurs within an interconnect device, such as an inside network interface device. A line isolation device (LID) houses the low pass filter and includes a communication jack for routing at least the ADSL signals to the transceiver unit. The LID also preferably includes a telephone jack for receiving the filtered POTS signals from the low pass filter and for providing a connection to a POTS terminal device. The LID is connected to a telephone jack within the customer""s wiring which has been modified so that it is connected to each of the blue, red, green, and yellow lines. In this manner, the modified telephone jack can route the incoming ADSL signals and POTS signals over the blue and yellow lines to the LID and can route filtered POTS signals from the LID to the other telephone jacks over the red and green lines.
The telephone jack for connecting the LID to the customer""s wiring preferably includes a connector having a pair of shorting bars. The shorting bars automatically short the blue and red lines together and short the green and yellow lines together when a mating connector from the LID is removed from the connector. In this manner, when the LID is disconnected from the customer""s wiring, the POTS signals are automatically routed from the blue and yellow lines to the red and green lines whereby all POTS terminal devices can continue to receive POTS signals over the red and green lines. When the mating connector from the LID is inserted into the connector, however, the shorting bars no longer short the lines together and the connector is able to carry the POTS signals and ADSL signals over the blue and yellow lines and is able to carry the filtered POTS signals over the red and green lines.
Accordingly, it is an object of the present invention to provide apparatus, systems, and methods which can easily add ADSL service to a customer""s wiring.
It is another object of the present invention to provide apparatus, systems, and methods which can easily remove ADSL service from a customer""s wiring.
It is a further object of the present invention to provide apparatus, systems, and methods for automatically switching between POTS only service and service for both POTS and ADSL.
It is yet another object of the present invention to provide apparatus, systems, and methods for low pass filtering all POTS signals in premises having ADSL service.
It is yet a further object of the present invention to provide apparatus, systems, and methods for isolating POTS signals from ADSL signals.